Many industrial systems in operation today have pipes or tubes designed to contain only air or other gases. Where a back-flow of liquids into such pipes or tubes can create harmful conditions, or where such back-flow might indicate an unwanted diversion of expensive or dangerous liquids, means of detecting liquid would be useful. Also, where the pipes or tubes contain radioactive materials or otherwise hostile environments, it is desirable to detect the presence of a liquid in the pipe or tube without penetrating the pipe or tube. Further difficulties are encountered in detecting liquids especially where the liquid back-flow may contain entrapped gas.
Techniques for sensing fluid presence in a pipe or tube include measuring the conductivity or capacitance of a fluid or measuring the attenuation of gamma, x-ray, visible or infra-red energy beams passed through a fluid. These techniques require costly equipment which is susceptable to damage or misalignment from rough handling. Further, these systems require continuous-wave excitation techniques which are susceptible to deleterious reflection signals.
A previous invention directed at this problem is U.S. Pat. No. 4,361,041, "Non-Intrusive Ultrasonic Liquid-In-Line Detector for Small Diameter Tubes", by Thomas C. Piper, issued Nov. 30, 1982. In that invention, two pairs of transducers are longitudinally displaced along a small pipe having a diameter of approximately 0.25 inches and a wall thickness of 0.035 inches. A tone generator connected to one pair of transducers sends a tone into the pipe via the first pair of transducers. Though suitable for pipes of such small diameter, the invention of '041 is less acceptable for larger diameter pipes because it did not provide a definitive signal with larger pipes. Furthermore, the '041 invention could render ambiquous results where liquid was only partially present in the line such as where there were bubbles or air gaps in the line between the sending and receiving pairs of transducers. A further disadvantage of the '041 invention was that when used with two transducers, the tubes had to be specially flattened to connect the transducers.
It is therefore an object of the present invention to detect the presence of liquid in a tube without penetrating the tube.
Another object of the present invention is to detect the presence of liquid in a tube without using continuous-wave excitation techniques.
An additional object of the invention is to provide an accurate and reliable liquid detection scheme that may be embodied in durable, relatively inexpensive equipment.
It is an additional object of the invention to provide a means for detecting the presence of liquid in a tube without having to modify the tube by drilling or flattening.
It is a further object of this invention to detect the presence of liquid in a tube of diameter larger than approximately 0.5 inch.
It is a still further object of this invention to detect the presence of liquid in a tube at an exact location in the tube.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.